I'm starting a thread for the beta testers to capture any bugs found, work around/fixes, and any tips or lessons learned while assembling and testing the GUS Simpson.

Bug:While assembling the arms, I found a problem with the alignment of the holes for mounting the stepper motor. It seemed like all of the holes were slightly (~0.2mm) too close to the shaft/spool opening, so I could only get one bolt to align to the threaded hole on the stepper motor. I was able to work around it by drilling the holes on the arm wider. I'm using the original lower arm that Nicholas posted in November, and I know he updated the file since, but I did not see any mention that this particular bug was addressed.

Bug:I could not apply enough pressure to drive the bolt that anchored the guitar tuning peg to the lower arm. The arch of the gear immediately above kept me from using a hex key wrench from above, and I could not apply enough pressure from the side to drive the bolt into the arm. I ended up drilling out the hole, coating the bolt with superglue, and press fitting it into the wider hole. This may not be a problem for everyone. I have fat fingers and was only using long nosed pliers and a simple hex key wrench. Perhaps better tools or someone more nimble hands will make this a non-issue.

Lesson Learned:If you are going to heat up your parts in an oven in order to easily push in the bearings, DO NOT handle the arms by the split gears. The soft plastic will deform and keep the gear teeth on the two arms from aligning properly.

Nicholas Seward wrote:By any chance did you print with ABS. I have about 10 arms around here that all line up.

Nope. I used a translucent red PLA for the arms. The plastic filament was cheap and had some problems with variation, but when I measured the parts after printing they matched the STLs. Is it possible they shrunk slightly when I baked them?

Changing the style of peg may help. There are versions of tuning pegs out there that use a stud instead of bolts to keep the peg from torquing, and a nut on the shaft to keep anchored. Unfortunately, these tend to get expensive. An example would be something like this:

It sounds like you are overdoing it in the oven. You might want to try the hot plate instead. Or stick then end in boiling water.

Good idea with the different pegs. I wish pegs were standardized so we didn't have to get locked in a particular brand. Maybe I can a mount block for the peg. This would allow the motor arm to be the same for every different type of peg. What do you think?

PeteD wrote:I'm starting a thread for the beta testers to capture any bugs found, work around/fixes, and any tips or lessons learned while assembling and testing the GUS Simpson.

Bug:I could not apply enough pressure to drive the bolt that anchored the guitar tuning peg to the lower arm. The arch of the gear immediately above kept me from using a hex key wrench from above, and I could not apply enough pressure from the side to drive the bolt into the arm. I ended up drilling out the hole, coating the bolt with superglue, and press fitting it into the wider hole. This may not be a problem for everyone. I have fat fingers and was only using long nosed pliers and a simple hex key wrench. Perhaps better tools or someone more nimble hands will make this a non-issue.

I also found this initially challenging, but eventually I got it with a ball driver. It could definitely be easier. Here are some possibilities:(1) Add to the BOM a longer m2x20 screw. Then you can form the thread from the reverse direction, so that when inserting it from within the cavity, it goes in more easily.(2) Similar idea to above, but enlarge the printbed-side hole to slightly larger than the m2 head diameter, so that the portion you thread remains just the length of the m2x10 screw Saves the need for a larger screw and reduce the time/hassle of threading a much longer hole.(3) Add a slight taper to the top entrance of the m2 hole to make it easier to start.

The downside to all these is that they still require a ball driver, but that may be a minor issue.

1.- The hub screw is not holding well against the hub bottom. I believe this is due to the normal use, the orientation of printing and its dimensions. Apparently, it is a little bit loose against the bottom and after some use it cannot hold all the pieces together. I tried using teflon tape but didn't work. The thread just got too round and now it slides. I'm considering making the screw and bottom out of aluminum.

2.- In the extruder, I cannot maintain the bearing in the "closed" position. The heads of the screws with springs keep getting out of the place. IMO, the recess for the heads is too small/printing artifacts don't let the heads get totally inside. It kinda worked in the beggining (but never getting totally inside), but with the use, the borders of the recesses got round and don't work anymore. The design is very good, and I believe this can be easily solved redesigning just the recess. Probably making it very wide and using a washer would help a lot.

1) I would do a scale in the xy direction using something like OpenSTL.

2) The latching is not ideal. I will try to redesign it to be a draw latch. This will allow you to operate it with one hand. Not sure on the time line for the redesign. I will probably get it done before the Midwest RepRap Festival.